The present invention relates to new and improved aluminum welding wire and more particularly to a metal-core aluminum welding wire which yields a high quality weld bead when used in welding components of aluminum articles.
Aluminum weld wire is conventionally provided as a solid wire that is generally produced by continuously casting round bars which are then heated to a temperature dependent on the alloy and rolled, for example, to ⅜ inch diameter. This rod is then drawn through a series of dies so that its diameter is reduced to the required size.
One of the problems that have been associated with weld deposits formed from aluminum weld wire is porosity. It is important that the weld beads be free of porosity. The porosity observed in aluminum welds has been attributed to a number of sources but one of the most prominent sources is voids caused by the release of hydrogen bubbles from the solidifying weld metal. These bubbles are caused by the introduction of hydrogen containing materials into the weld bead. During the welding, hydrogen-containing materials are decomposed and the hydrogen so produced dissolves in the molten metal. Upon solidification, the lower solubility of the hydrogen in the solid metal results in the rejection of hydrogen in solution and the production of small voids in the weld. It has been reported that hydrogen-containing materials may enter the weld bead from a number of sources but one of the principal sources is the welding wires themselves.
U.S. Pat. No. 3,676,309 discloses an aluminum base alloy welding wire, which is coated with an alumina-phosphate coating having a low rate of hydration such that essentially porosity free welds are obtained. The aluminum welding wire may be prepared by immersing the wire in a first aqueous alkaline solution containing an anode strip, continuously immersing the wire in a second aqueous alkaline solution containing a cathode strip, and passing an electric current through the electrolytes while the wire is immersed therein. Thereafter the wire may be rinsed in cold water, immersed in a passivating and neutralizing acid bath, and again rinsed. The second part of the process is an acid electrolytic treatment.
U.S. Pat. No. 4,913,927 discloses an aluminum weld wire having an ultra clean aluminum surface, lubricated with a dual coating of an essentially anhydrous lower alkanol and a colloidal solid lubricant.
Japan Patent Publication (OPI) 6-304780-A to Isuzu Motors Ltd. K.K. discloses an aluminum weld wire that is tubular and filled with a flux. According to the publication the flux contains 5-10% sodium, 40-45% potassium, 5% or less oxygen, 5% or less sulfur, 5-10% fluorines, and 35-40% chlorines.